Oxygen demand is a parameter that can be used to assess the concentration of organic pollutants in water resources. As microorganisms in the environment consume these materials, oxygen is depleted from the water. Chemical oxygen demand (COD), biological oxygen demand (BOD), and total organic carbon (TOC) are three indices that can be used to assess the level of organic pollution in aqueous systems. TOC analysis can be used for organic compounds, and BOD can be used to reflect biodegradable portions of the pollutants. COD is commonly used to represent the pollution level of waste waters. COD can be defined as the amount of oxygen consumed in the oxidation of organic compounds by strong oxidizing agents.